The present invention relates generally to methods and compositions for monitoring the processing of β-amyloid precursor protein. More particularly, the present invention relates to the use of such methods and compositions for the diagnosis, prognosis and monitoring response to therapy of Alzheimer's disease and other beta-amyloid related diseases as well as to the use of the disclosed antibodies in passive immunization as a method for treatment of Alzheimer's disease and other beta-amyloid related diseases.
Alzheimer's Disease (AD) is a degenerative brain disorder characterized clinically by progressive loss of memory, cognition, reasoning, judgment and emotional stability that gradually leads to profound mental deterioration and ultimately death. AD is a very common cause of progressive mental failure (dementia) in aged humans and is believed to represent the fourth most common medical cause of death in the United States. AD has been observed in races and ethnic groups worldwide and presents a major present and future public health problem. The disease is currently estimated to affect about two to three million individuals in the United States alone. AD is at present incurable. No treatment that effectively prevents AD or reverses its symptoms and course is currently known.
The brains of individuals with AD exhibit characteristic lesions termed senile (or amyloid) plaques, amyloid angiopathy (amyloid deposits in blood vessels) and neurofibrillary tangles. Large numbers of these lesions, particularly amyloid plaques and neurofibrillary tangles, are generally found in several areas of the human brain important for memory and cognitive function in patients with AD. Smaller numbers of these lesions in a more restricted anatomical distribution are also found in the brains of most aged humans who do not have clinical AD. Amyloid plaques and amyloid angiopathy also characterize the brains of individuals with Trisomy 21 (Down's Syndrome), Diffuse Lewy Body Disease and Hereditary Cerebral Hemorrhage with Amyloidosis of the Dutch-Type (HCHWA-D).
A major constituent of amyloid plaques are a variety amyloid-beta (Aβ) peptides which are produced by cleavage of the β-amyloid precursor protein (APP). While in the past there was significant scientific debate over whether the plaques and tangles are a cause or are merely the result of Alzheimer's disease, recent discoveries indicate that amyloid plaque is a causative precursor or factor. In particular, it has been discovered that the production of Aβ peptides can result from mutations in the gene encoding amyloid precursor protein, a protein which when normally processed will not produce the Aβ peptides. The identification of mutations in the amyloid precursor protein gene which cause familial, early onset Alzheimer's disease is the strongest evidence that amyloid metabolism is the central event in the pathogenic process underlying the disease. It is presently believed that a normal (non-pathogenic) processing of the APP protein occurs via cleavage by an “alpha.-secretase” which cleaves between amino acids 16 and 17 of the Aβ peptide region within the protein. It is further believed that pathogenic processing occurs in part via “beta.-secretases” which cleave at the amino-terminus of the Aβ peptide region within the precursor protein.
Recently, it was demonstrated that BACE-1 is the major β-secretase required for cleavage of APP at position +1 and that overexpression of BACE-1 results in an additional cleavage at the +11 site of the Aβ, generating shorter Aβ11-40 and Aβ11-42 fragments, hereinafter also referred to as the Aβ11-x peptides. These Aβ peptides have been detected in conditioned medium of primary rat neuronal cell cultures and mouse N2a cells, suggesting that they are normal APP cleavage products generated in neurons (3, 4, 5). Significantly, these shorter Aβ fragments have also been identified as major species in AD brains and normal aging brains by biochemical analysis (6) as well as in Down syndrome brains with AD pathology by immunohistochemistry studies (7). This event calls for a re-evaluation of the role of Aβ11-40/42 in the pathogenesis of Alzheimer's disease, especially in view of the fact that Aβ species beginning at Glu11 prove to be more insoluble than those beginning at position 1 of Aβ.
Despite the progress which has been made in understanding the underlying mechanisms of AD and other Aβ-related diseases, there remains a need to develop methods and compositions for diagnosis and treatment of the disease(s). Thus, the ability to monitor cellular processing of the amyloid precursor protein would be of significant value in the diagnosis, prognosis, and therapeutic supervision of Alzheimer's disease. In particular, it would be desirable to identify minimally invasive reproducible procedures for screening and evaluating detectable diagnostic markers in readily obtainable patient samples, such as serum, cerebrospinal fluid (CSF), and the like. Polyclonal antibodies such as the ones described by Said T. C., et al., Neuroscience Letters 215 (1996); 173-176 are useful to detect the different Aβ-peptides in biological samples but given the fact that each batch of polyclonal antibodies is different, these antibodies do not provide the tools to perform reproducible procedures for screening and evaluating detectable diagnostic markers in readily obtainable patient samples. In addition, the non-specific binding using polyclonal antibodies, is typically higher and the accuracy in Western blotting is typically lower.
A number of potential diagnostic markers for Alzheimer's disease have been proposed. Of particular interest to the present invention are the shorter carboxy-terminal fragments of the Aβ precursor protein obtained after beta-secretase cleavage of the APP protein. These markers should be useful by themselves and/or in combination with other diagnostic markers and procedures. Preferably, the diagnostic markers would be detectable in body fluids, such as CSF, blood, plasma, serum, urine, tissue, and the like, so that minimally invasive diagnostic procedures can be utilized.
Specific assays for Aβ11-x detection should be capable of detecting Aβ11-x in fluid samples at very low concentrations in a reproducible and consistent manner as well as distinguishing between Aβ11-x peptides and other fragments of APP, which may be present in the sample.
These and other aspects of the invention are described herein in more detail.